1. Field of the Invention
The present invention relates to a technique for learning a reference position of a camshaft in a variable valve-timing controlling system in which a rotational phase of the camshaft relative to a crankshaft of an internal combustion engine.
2. Description of the Related Art
Hitherto, a variable valve-timing controlling system for an internal combustion engine is known, in which a rotational phase of a camshaft relative to a crankshaft of the engine is varied so as to adjustably change valve timing of an intake and/or an exhaust valve of the engine (refer to Laid-open Japanese Patent Publication No. 11-082073 (JPP-""073)).
More specifically, in the variable valve timing controlling system of JPP-""073, there are provided a crank angle sensor for generating N pulse signals as per one complete rotation of the crankshaft, and a cam sensor for generating 2N pulse signals as per one complete rotation of the intake valve side camshaft, and on the basis of a relative rotational angle between the pulse signals from the crank angle sensor and the pulse signals from the cam sensor, the rotational phase of the camshaft relative to the crankshaft is detected.
Further, in the variable valve timing controlling system of JPP-""073, the relative rotational phase detected when the camshaft is at the most retardant position which is a reference position, is stored as a learned value for the most retardant position of the camshaft, to detect the rotational phase of the camshaft relative to the crankshaft with this learned value as a reference.
The aforementioned cam sensor generates 2N pulse signals as per one complete rotation of the cam shaft by detecting 2N detection subjects arranged equiangularly in the rotation direction of the camshaft. However, depending on machining errors, there may appear inequality in the angular spaces between the respective neighboring detection subjects.
If there appear any inequality in the angular spaces, even if an actual rotational phase of the camshaft relative to the crankshaft is the same, the results of detection of the rotational phase become different from each other due to the detection subjects to be used. Therefore, a problem occurs such that accuracy in the learning of the reference position of the camshaft will be unavoidably lowered.
Therefore, an object of the present invention is to provide a reference position learning apparatus and method of a variable valve timing controlling system, which is able to improve the learning accurately of a reference position for variable valve timing control (a VTC reference position) and also to ensure an appropriate responsibility in a feedback controlling of valve timing.
In order to achieve the above object, with the present invention, in a constitution where there are provided a crank angle sensor that generates a rotation-detection signal of the crankshaft, and a cam sensor that detects a plurality of detection subjects provided for the camshaft so as to be arranged in a rotating direction of the camshaft, to generates a rotation-detection signal for each of the plurality of detection subjects, and the rotational phase of the camshaft relative to the crankshaft is detected on the basis of the rotation-detection signals of the crank angle sensor and the cam sensor, to feedback control a variable valve timing system on the basis of the detected rotational phase,
a rotational phase of the camshaft corresponding to a reference position of the camshaft is learned during the stopping of the feedback control and a rotational phase is detected with the learned value as a reference, and
when learning the reference position, a detection result of the rotational phase is smoothened more effectively than a detection result of the rotational phase during the feedback control, to learn the rotational phase corresponding to the reference position on the basis of the smoothened detection value of the rotational phase.
The above and other objects, features and advantages of the present invention will become apparent from the following description of several preferred embodiments thereof, with reference to the accompanying drawings.